Recent studies have confirmed that there is an association between maternal periodontal disease and pregnancy complications that result in premature delivery [e.g. gestational age (GA)<37 weeks: adjusted odds ratio 2.1(CI95%:1.12, 4.09)and OR=4.2 for GA<28 weeks (CI95%: 1.42,12.6)] and decreased fetal weight [e.g. among mothers with births of GA between 35-37 weeks, those with periodontal disease (4+ sites with 5+mm PD and 2+mm AL) have neonates that are 13.8% smaller (p=0.004). The deleterious effect of maternal periodontal infection on pregnancy is particularly pronounced among African Americans and may, in part, account for some of the disparities in the prevalence of these unfortunate complications. Not only does the presence of periodontal disease early in pregnancy confer risk, but the worsening of periodontal disease during pregnancy - a relatively frequent event (35.5% of 814 deliveries) appears to independently enhance the risk of fetal exposure to periodontal pathogens (as evidenced by fetal cord blood IgM antibody to maternal oral pathogens) and preterm birth (OR=5.0, CI95%:2.22,11.3). These data suggest that periodontal disease and its progression may represent an infectious and inflammatory exposure that could have serious deleterious effects during pregnancy. Scientifically, to determine whether periodontal disease is causally related to preterm delivery and confers any modifiable risk, it will be critical to demonstrate that treating periodontal disease in pregnant mothers results in a decreased incidence of preterm birth and growth restriction. It is our central hypothesis that mothers with periodontitis that receive periodontal treatment during the second trimester of pregnancy will experience a lower rate of preterm delivery and a higher mean birth weight of the premature infants. We propose to conduct a 5-year randomized, 2-armed, clinical trial completing 1800 mothers at 3 medical/dental centers (UNC/Duke, UAB & UTHSCSA) that combine both periodontal and Obstetrics/Gynecology clinical trial expertise. We propose to randomly assign 1800 pregnant mothers with periodontal disease to one of two treatment arms 1) scaling and root planning during the second trimester or 2) scaling and root planning post-partum. Biological samples will be collected and archived during the conduct of the study to enable future investigations that will seek to further elucidate the role of maternal oral and vaginal infections on pregnancy. We hypothesize that periodontal treatment during pregnancy will significantly reduce the incidence of preterm deliveries of GA<35 weeks and also enhance the mean weight of those of GA<37 weeks. The impetus for this study is further supported by results from a pilot study conducted at UAB that demonstrated that scaling and root planning reduced the rate of GA<35 weeks from 6.4% in the untreated group to 0.81%. This application entitled MOTOR (Maternal Oral Therapy to Reduce Obstetric Risk) includes 5 separate components: an administrative oversight project (UNC Dental School), 3 clinical trial performance sites (UNC Dental/Duke Medical, UAB Dental & Medical and UTHSCSA Dental & Medical) and a clinical trials data and statistical coordinating center (UNC Collaborative Studies Coordinating Center, School of Public Health).